Spiroperidol Binding Research Articles

3H]Haloperidol and [3H]spiroperidol binding in rat striatum during ageing.

3H]Haloperidol and [3H]spiroperidol binding in rat striatum during ageing.

Dopamine receptor changes after long-term haloperidol treatment in rats.

Abstract Tardive dyskinesia is a neurological syndrome associated with prolonged neuroleptic treatment of schizophrenic patients (Crane 1968; Faurbye 1970; Faurbye et al 1964). It has been suggested that tardive dyskinesia results from chemical denervation of central dopamine neurons and subsequent development of supersensitivity of the postsynaptic receptor (Rubovits & Klawans 1972). Experiments based on animal models of tardive dyskinesia support this hypothesis. Chronic neuroleptic treatment increases postsynaptic dopamine receptor sensitivity when measured either behaviourally or biochemically (Christensen et al 1976; Klawans & Rubovits 1972; Moore & Thornburg 1975; Sayers et al 1975; Tarsy & Baldessarini 1974; Von Voigtlander et al 1975). The molecular basis for this behavioural change has been reported to be an increase in the number of receptor sites with no change in their affinity as measured by 3H-neuroleptic binding to striatal membrane homogenates (Burt et al 1977; Klawans et al 1977; Muller & Seeman 1977). Previous biochemical reports of the development of model tardive dyskinesia after neuroleptic treatment of animals have generally used treatment periods of 3 weeks or less (Burt et al 1977; Klawans et al 1977; Muller & Seeman 1977). Only one report treated animals for longer periods (Clow et al 1978). In the present experiments we studied the kinetics of [3H]spiroperidol binding to rat caudate nucleus homogenates after 3 and 10 weeks of haloperidol treatment.

Differential effects of cocaine-induced seizures and lethality on M(1)-like muscarinic and dopaminergic D (1)- and D (2)-like binding receptors in mice brain.

This work was designed to study the changes produced by cocaine-induced seizures and lethality on dopaminergic D(1)- and D(2)-like receptors, muscarinic M(1)-like binding sites, as well as acetylcholinesterase activity in mice prefrontal cortex (PFC) and striatum (ST). Binding assays were performed in brain homogenates from the PFC and ST and ligands used were [(3)H]-N-methylscopolamine, [(3)H]-NMS (in the presence of carbachol), [(3)H]-SCH 23390 and [(3)H]-spiroperidol (in presence of mianserin), for muscarinic (M(1)-like), D(1)- and D(2)-like receptors, respectively. Brain acetylcholinesterase (AChE) activity was also determined in these brain areas. Cocaine-induced SE decreased [(3)H]-SCH 23390 binding in both ST and PFC areas. A decrease in [(3)H]-NMS binding and an increase in [(3)H]-spiroperidol binding in PFC was also observed. Cocaine-induced lethality increased [(3)H]-spiroperidol binding in both areas and decreased [(3)H]-NMS binding only in PFC, while no difference was seen in [(3)H]-SCH 23390 binding. Neither SE, nor lethality altered [(3)H]-NMS binding in ST. AChE activity increased after SE in ST while after death the increase occurred in both PFC and ST. In conclusion, cocaine-induced SE and lethality produces differential changes in brain cholinergic and dopaminergic receptors, depending on the brain area studied suggesting an extensive and complex involvement of these with cocaine toxicity in central nervous system.

Postnatal haloperidol eliminates the deficit in circling behavior produced by prenatal exposure to the same drug

Up to 35% of pregnant women take psychotropic drugs at least once during gestation [Austin and Mitchell, 1998]. From concurrent animal and human evidence, it has been proposed that exposure to several psychoactive medications in utero or during lactation increases the risk for permanent brain disorders . Present preventive or therapy practices applied on humans for this type of long-lasting behavioral alterations are mainly based on empirical results. Here, we test an experimental approach designed to counteract a circling performance deficit that appears in Sprague–Dawley rats at puberty on exposure to the dopaminergic blocker haloperidol (HAL) during gestation [J.L. Brusés, J.M. Azcurra, The circling training: A behavioral paradigm for functional teratology testing, in: P.M. Conn (Ed.), Paradigms for the study of behavior, Acad. Press, New York, 1993, pp. 166–179. Method Neurosci. 14]. Gestational exposure to HAL (GD 5–18, 2.5 mg/kg/day ip) induced the expected circling activity decrease in the offspring at the fifth week of life. When prenatal exposure to HAL was continued through lactation (PD5–21, 1.5 mg/kg/day ip), rats otherwise showed a control-like circling performance. No difference was yet found between lactation-only, HAL-exposed pups and saline (SAL)-treated controls ( n=8 each group). We further performed saturating ( 3H)-spiroperidol (SPI) binding assays on striatal P2 membrane fractions 2 months later. The dopamine-type D2-specific binding results suggested that above circling behavior findings could be partially explained by enduring HAL-induced neurochemical changes. The role of critical periods of sensitivity as transient windows for opportunistic therapies for behavioral teratology is discussed.

Occurrence of Dopaminergic (D2) Receptors within the Rabbit Pulmonary Circulation

The pharmacological characteristics and the microanatomical localization of dopamine D2-like receptors, or more correctly spiroperidol binding sites, in the rabbit pulmonary circulation were studied using combined marker binding and light microscopy autoradiography with [3H]-spiroperidol (spiperone) as marker. The marker was bound to the samples of the pulmonary artery in a manner consistent with the labelling of dopamine D2-like receptors with an equilibrium dissociation constant (Kd) of about 2.4±0.07nmol/l and a maximum density of binding sites of 65±4.5fmol/mg tissue. Samples of bronchial artery show the same results as those of the pulmonary artery. In contrast, binding experiments made with samples of rabbit lung (capillary of the microcirculation), of pulmonary veins and/or of bronchial veins did not allow the evaluation of specific binding.Autoradiography, observed with light microscopy, showed the development of specific silver grains within the whole wall of extraparenchymal branches of the pulmonary artery and/or of the bronchial artery. Development of silver grains was inhibited by compounds active on the dopamine receptors. The greater sensitivity to displacement by domperidone, haloperidol, and bromocriptine than to displacement by N-propyl-nor-apomorphine, quinpirole and clozapine suggests that the binding sites observed in extraparenchymal, large and medium-sized branches of the rabbit pulmonary and bronchial arteries belong, likely, to the dopamine D2 receptor subtype. Quantitative analysis of images let us count the amount of these receptors in many samples of the pulmonary and/or bronchial arteries.

Altered Regulation of Dopaminergic Activity and Impairment in Motor Function in Rats After Subchronic Exposure to Styrene

Animal and human studies suggest a dopamine-mediated effect of styrene neurotoxicity. However, the results reported to date are incomplete and not consistent. As such, the mechanism of its neurotoxicity is still unclear. The present study has, therefore, reexamined the central dopaminergic system in relation to some neurobehavioral effects in rats following subchronic exposure to styrene. Groups of adult male Sprague–Dawley rats received 0, 0.25, or 0.5 g styrene per kg b.wt. by gavage for 13 consecutive weeks. Twenty-four hours after cessation of such treatment with the higher dose (0.5 g/kg), the contents of dopamine (DA) and its metabolites were significantly reduced in the corpus striatum, hypothalamus, and lateral olfactory tract regions. In vitro styrene showed a significant increase in DA release from rat striatal synaptosomes similar to that of tyramine. Significant loss of motor function was observed on days 56, 70, and 84 during the styrene treatment with the higher dose, and lasted over a month after such treatment. However, the treated animals recovered their motor function within 45–60 days after cessation of such treatment, along with the recovery of normal levels of dopamine and its metabolites. Furthermore, styrene-induced initial impairments in measures of dopaminergic activity cannot be attributed to altered regulation of tyrosine hydroxylase activity. Specific [ 3H]-spiroperidol binding was also unaltered 7 or 15 days after subchronic treatment with styrene. These data imply that despite the dopaminergic neuronal loss due to styrene, dopaminergic transmission was not reduced to a level that would result in an overall development of dopamine receptor supersensitivity in the striatum. Collectively, these studies indicate that the subchronic neurotoxic action of styrene may be primarily presynaptic in nature and may involve impaired regulation of DA content and stimulation of DA release.

Early Withdrawal From Repeated Cocaine Administration Upregulates Muscarinic and Dopaminergic D2-Like Receptors in Rat Neostriatum

The present results show an increase in locomotor activity 24 h following repeated cocaine administration only with the higher dose (10 mg/kg, IP, daily for 1 week) compared to controls (administered with saline). Binding assays were done and the ligands used were [3H]N-methylscopolamine ([3H]-NMS), [3H]-SCH 23390, and [3H]-spiroperidol to determine muscarinic (M1- and M2-like), D1 and D2 receptors, respectively. Scatchard analyses revealed alterations in Bmax not only for muscarinic, but also for D2-like receptors that were significantly increased. On the other hand, no alterations were detected on D1-like receptors densities and dissociation constant values. However, the Kd value was significantly increased for D2 receptors. The changes in muscarinic receptors were observed predominantly on M2-like, which presented an increase of 84% with the 10 mg/kg, IP, dose only. On D2-like receptors, increases of 63 and 54% were demonstrated with the doses of 5 and 10 mg/kg, IP. The preferential effects of cocaine on muscarinic and D2-like receptors were also demonstrated in vitro where decreases in [3H]-NMS and [3H]-spiroperidol binding were observed. The results indicate that the effects of cocaine on muscarinic and dopaminergic postsynaptic receptors are functions of dose, duration of treatment, and time of drug withdrawal.

Modulation of Dopamine D<sub>2</sub> Receptor Expression by an NMDA Receptor Antagonist in Rat Brain

The expression of dopamine D2 receptor mRNA was studied in rat brain following micro-injection of a competitive N-methyl D-aspartate (NMDA) receptor antagonist at the prefrontal cortex. Male Sprague-Dawley rats cannulated bilaterally into the medial prefrontal cortex were injected with a competitive NMDA receptor antagonist (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP). The levels of mRNA for NMDA-R1 and dopamine D2 receptors were measured by reverse transcriptase-polymerase chain reaction (RT-PCR), and D2 receptor density was quantified by [3H]spiperone binding in the cortex and striatum of these animals. In the prefrontal cortex, the levels of NMDA-R1 receptor mRNA showed significant decrease in CPP-treated animals compared to control animals. However, NMDA-R1 mRNA levels in striatum remained unchanged in any of the experimental groups. The D2 receptor mRNA levels and [3H]spiroperidol binding in prefrontal cortical membranes showed no significant difference between the CPP-treated and control groups of animals. In the striatum, a significant increase in striatal dopamine D2 receptor mRNA levels was shown in animals treated with CPP. The increase in D2 mRNA level was correlated with an increase in the D2 receptor binding sites in the striatal membranes. These results suggest a possible interaction between prefrontal cortical NMDA receptors and striatal dopamine receptors.

Modulatory role of dopamine on excitatory amino acid receptors

1. 1. In extensively washed synaptic membrane preparations from rat prefrontal cortex, the “ in vitro” addition of either the d 1 (SKF 38393) or the D 2 (LY 171555) specific agonists markedly decreased the apparent affinity of the NMDA receptor antagonist [ 3H]-MK801 specific binding. In the same membrane preparation, the concentration of L-glutamate required to produce half maximal enhancement of [ 3H]-MK801 binding was approximately the same both in the presence or in the absence of dopaminergic drugs. 2. 2. I.c.v. administration of the neurotoxin 6-OHDA resulted in a dramatic reduction of dopamine (DA) prefrontal cortex levels, whilst repeated administrations (21 consecutive days) with either the D 1 (SCH 23390) or the D 2 (YM 09151-2) selective antagonist failed to change DA and DOPAC contents. 3. 3. Repeated administrations with the d 1 receptor Mocker SCH 23390 selectively increased the Bmax values of [ 3H]-SCH 23390 binding while [ 3H]-spiroperidol binding was increased both by repeated administrations of YM 09151-2 and by i.c.v. injection of 6-OHDA. 4. 4. Although both chronic D 2 blockade and 6-OHDA lesions consistentely increased D 2 receptor number, in extensively washed synaptic plasma membranes (SPM) of rats repeatedly administered with YM 09151-2 but not with 6-OHDA, the [ 3H]-mk801 binding was increased. 5. 5. It is concluded that the effects of NMDA receptor activation could not be directely mediated by stimulation of DA release, but are highly dependent upon the presence of DA axon terminals.

Effects of monoamine uptake inhibitors given early postnatally on monoamines in the brain stem, caudate/putamen and cortex, and on dopamine D1 and D2 receptors in the caudate/putamen.

Rats were treated with desipramine 5 mg/kg, nomifensine 10 mg/kg, zimelidine 25 mg/kg or with 0.9% sodium chloride once a day during the second and third weeks after birth, and brain stem, caudate/putamen and cortical monoamines, and caudate/putamen dopamine D1 (3[H]SCH 23390) and D2 (3[H]spiroperidol) receptor binding were measured when rats were at two months of age. In the brain stem, the concentration of 3-methoxy-4-hydroxy-phenyl glycol was increased in nomifensine rats and the ratio of 5-hydroxyindoleacetic acid to 5-hydroxytryptamine was increased in zimelidine rats. In the caudate/putamen, the concentrations of 3,4-dihydroxyphenylacetic acid and homovanillic acid and the ratio of homovanillic acid to dopamine were increased in desipramine rats; neither 3[H]SCH 23390 nor 3[H]spiroperidol binding were affected by any of the three monoamine uptake inhibiting antidepressants studied. In the cortex, the ratio of 5-hydroxyindoleacetic acid to 5-hydroxytryptamine was increased in desipramine and zimelidine rats. The findings suggest that desipramine but not nomifensine increases the metabolism of dopamine in the caudate/putamen and nomifensine but not desipramine increases the metabolism of norepinephrine in the brain stem, and furthermore that the metabolism of serotonin is affected by desipramine as well as by zimelidine. It is possible that also treatment of women with these drugs during late pregnancy causes long-lasting changes in the brain of human fetus.

Autoradiographic localization of dopamine D2-like receptors in the rat adrenal gland.

The pharmacological profile and the anatomical localization of dopamine D2-like receptors were studied in sections of the rat adrenal gland using combined radioligand binding and autoradiographic techniques with [3H]-spiroperidol as a ligand. [3H]-Spiroperidol was bound to sections of the rat adrenal gland in a manner consistent with the labelling of dopamine D2-like receptor sites. The binding was time-, temperature- and concentration-dependent and of high affinity with a dissociation constant (Kd) value of 1.6 +/- 0.04 nM and a maximum density of binding sites (Bmax) of 60 +/- 3.6 fmol/mg tissue. Experiments on the pharmacological specificity of [3H]-spiroperidol binding to sections of the rat adrenal gland suggest the labelling of dopamine D3 and/or D4 receptors. The presence of dopamine D3 and D4 receptors in the rat adrenal gland was confirmed by the demonstration of a specific binding for the D3 radioligand [3H]-7-hydroxy-N,N-di-n-propyl-2-aminotetralin (DPAT) and for the D4 radioligand [3H]-clozapine. Light microscope autoradiography showed the highest accumulation of silver grains which correspond to [3H]-spiroperidol binding sites in the rat adrenal medulla. In the adrenal cortex, where density of silver grains is about 40% lower than in the medulla, the radioligand is accumulated primarily in the zona glomerulosa and to a lesser extent in the zona reticularis. These findings suggest that dopamine D2-like receptor sites in the rat adrenal gland cortex are primarily involved in the modulation of catecholamine secretion from the medulla and of aldosterone secretion from the cortex. The possible relevance of the occurrence of dopamine D3 and D4 receptor subtypes in the adrenal gland is discussed.

Localisation of dopamine D 2-like receptors in pulmonary artery of the human and rabbit but not of the rat

The present study was designed to investigate the presence of dopamine D 2-like receptor sites in the main trunk of the human, rabbit and rat pulmonary artery using combined radioligand binding and light microscope autoradiography techniques. [ 3H]Spiroperidol was used as a ligand. The presence and the localisation of the sympathetic neuroeffector plexus were also studied using catecholamine histofluorescence techniques. Radioligand binding experiments demonstrated the labelling of a population of dopamine D 2-like receptors in sections of human and rabbit pulmonary arteries by [ 3H]spiroperidol. No specific binding occurred in sections of the rat pulmonary artery. Light microscope autoradiography showed the development of specific silver grains within the tunica adventitia, including the adventitia-media border, of the human and rabbit pulmonary arteries. No specific silver grains were found in sections of the rat pulmonary artery. Studies on the pharmacological characterisation of [ 3H]spiroperidol binding sites in the human and rabbit pulmonary arteries showed that they are sensitive primarily to domperidone, haloperidol, (-)-sulpiride or bromocriptine, and to a lesser extent to n-propylnorapomorphine, quinpirole or clozapine displacement. This suggests that [ 3H]spiroperidol binding sites in the pulmonary artery probably belong to the dopamine D 2 receptor subtype. Catecholamine histofluorescence techniques revealed a rich plexus of fluorescent adventitial and adventitial-medial nerve fibres in the human and to a lesser extent in the rabbit pulmonary artery. Comparison of the localisation of dopamine D 2-like receptor sites and of the sympathetic neuroeffector plexus in the pulmonary artery, suggests a possible prejunctional localisation of these sites.

Pharmacological characterization and autoradiographic localization of dopamine receptors in the human adrenal cortex

The pharmacological characteristics and the anatomical localization of dopamine D1-like and D2-like receptors were studied in sections of the human adrenal cortex using radioligand binding and autoradiographic techniques. [3H]SCH 23390 was used as a ligand of D1-like receptors, whereas [3H]spiroperidol was used to label D2-like receptors. No specific [3H]SCH 23390 binding was detectable in sections of the human adrenal cortex. On the other hand, [3H]spiroperidol was bound to sections of the adrenal gland in a manner consistent with the labelling of dopamine D2-like receptor sites. The binding was time, temperature and concentration dependent, belonging in the range of concentrations of the radioligand used for a single class of high-affinity sites. The dissociation constant (Kd) averaged 2.7 nmol/l, whereas the maximum density of binding sites (Bmax) was 160 nmol/mg tissue. Experiments on the pharmacological specificity of [3H]spiroperidol binding to sections of the human adrenal cortex revealed that clozapine was the most powerful displacer of [3H]spiroperidol from sections of the human adrenal cortex. This suggests the presence in the human adrenal cortex of dopamine receptors of the D4 subtype. Light microscope autoradiography showed the highest density of specific [3H]spiroperidol binding sites in the zona glomerulosa and to a lesser extent in the zona reticularis. Only sparse [3H]spiroperidol binding sites were localized in the zona fasciculata. The possible functional consequences of this localization of dopamine D2-like receptor sites in the human adrenal cortex are discussed.

Autoradiographic localization of dopamine D2-like receptors in the rabbit pulmonary vascular tree.

In the present study, the pharmacological characteristics and the anatomical localization of dopamine D2-like receptor sites in the extraparenchymal and in the intraparenchymal portion of the rabbit pulmonary artery were investigated using combined radioligand binding and light microscope autoradiography with [3H]-spiroperidol (spiperone) as a ligand. The ligand was bound to sections of the pulmonary artery in a manner consistent with the labelling of dopamine D2-like receptors with an equilibrium dissociation constant (Kd) of about 2.4 +/- 0.07 nmol/l and a maximum density of binding sites of 65 +/- 4.5 fmol/mg tissue. In contrast, binding experiments made with sections of rabbit lung did not allow the evaluation of specific binding. Light microscope autoradiography showed the development of specific silver grains within the tunica adventitia of extraparenchymal branches of rabbit pulmonary artery and of large and, to a lesser extent, of medium-sized intraparenchymal branches of the pulmonary artery. No silver grains were found within small branches of the pulmonary artery or of the pulmonary vein. Development of adventitial silver grains was inhibited by compounds active at dopamine receptors. The greater sensitivity to displacement by domperidone, haloperidol, (-)-sulpiride and bromocriptine than to displacement by N-propyl-norapomorphine, quinpirole or clozapine suggests that the [3H]-spiroperidol binding sites observed in extraparenchymal, large and medium-sized branches of the pulmonary artery belong, probably, to the dopamine D2 receptor subtype. The possible pre-junctional localization of these sites is discussed.

Antisense strategy unravels a dopamine receptor distinct from the D2 subtype, uncoupled with adenylyl cyclase, inhibiting prolactin release from rat pituitary cells.

The antisense strategy was used to unravel the functional contribution of the mRNAs encoding dopamine (DA) receptors to the multiple transduction mechanisms operated by DA in rat pituitary cells. An antisense oligonucleotide was designed to recognize seven nucleotides upstream and 11 nucleotides downstream from the initiation translation codon of the mRNA that encodes the DA D2 receptor. Addition of the antisense oligonucleotide for 7 days to primary culture of rat pituitary cells resulted in a decreased expression of DA D2 receptor as shown by (a) the virtual disappearance of [3H]spiroperidol binding sites and (b) the marked reduction in the levels of both the long and the short splice variant of the D2 receptor mRNAs. After this treatment, the DA D2 receptor agonist bromocriptine lost its capability both to inhibit adenylyl cyclase activity and to reduce prolactin mRNA levels. On the contrary, the inhibition of prolactin release induced by bromocriptine was affected minimally by the antisense oligonucleotide treatment. These data indicate that (a) translation of the mRNA encoding DA D2 receptors results in receptors that are negatively coupled with adenylyl cyclase and functionally linked to inhibition of prolactin synthesis; and (b) the release of prolactin might be regulated, at least in part, by a DA receptor that is encoded by mRNA species distinct from those encoding the D2 receptor.

The limbic functional selectivity of amperozide is not mediated by dopamine D 2 receptors as assessed by in vitro and in vivo binding

Behavioural, biochemical and electrophysiological studies suggest that amperozide affects mesolimbic dopamine neurotransmission. Amperozide is a potent 5-HT 2 receptor antagonist with only a moderate affinity for rat brain dopamine D 2 receptors. The brain regional dopamine D 2 receptor binding properties of amperozide were investigated by using in vitro and in vivo radioligand binding techniques. Amperozide displaced [ 3H]spiroperidol binding from rat striatal and limbic dopamine D 2 receptors with moderate affinity ( K i = 540 ± 118 nM and K i = 403 ± 84 nM, respectively). The dopamine D 2 receptor antagonist l-sulpiride and the agonist dopamine did not show different affinity in the two brain regions. Amperodize potently displaced in vivo [ 3H]spiroperidol binding in rat frontal cortex (ID 50 = 1.4 mg/kg s.c.) but was devoid of effect in striatum, olfactory tubercle and nucleus accumbens (ID 50 > 100 mg/kg s.c.). Chronic administration of amperozide (5 mg/kg p.o) for three weeks did not result in any change of maximal dopamine D 2 receptor number in either striatal or limbic tissue. The effects of amperozide on dopamine neurotransmission are thus not likely to occur by a direct interaction with dopamine D 2 receptors in either striatal or limbic tissue. The functional limbic selectivity might rather be mediated by serotoninergic pathways.

A new animal model of dopamine supersensitivity using s.c. implantation of haloperidol releasing polymers

Dopamine supersensitivity was induced by either the continuous daily release of 1.0 mg/kg haloperidol from controlled release polymers implanted subcutaneously in rats or by daily bolus injection. In vitro, these polymers were found to release haloperidol for more than 250 days. After implantation in vivo, supersensitivity was quantified by locomotor activity following apomorphine injection and specific [ 3H]spiroperidol binding to striatal synaptic membranes. Supersensitivity in rats with haloperidol implants was remarkably similar to that evoked by daily drug applications after 3 weeks without producing the detrimental daily sedations, typically seen after bolus administration. Furthermore, no difference in specific binding between both group was seen. A continuous delivery of haloperidol for 8 weeks also resulted in comparable denervation supersensitivity. Controlled release polymers may thus be a superior tool to induce denervation supersensitivity in a gradual, continuous fashion.

Prevention and reversal of dopamine receptor supersensitivity by cyclo(leucyl-glycyl) (CLG): Biphasic dose-response curves

Chronic administration (21 days) of haloperidol (HAL) (IP, 1.0 mg/kg/day) induced a behavioral supersensitivity (stereotypic sniffing) to dopamine (DA) agonists (apomorphine) and upregulation (increased B max for sulpiride-inhibitable [ 3H]spiroperidol binding) of striatal and limbic D 2 DA receptors (DAr). Coadministration of cyclo(leucyl-glycyl) (CLG; 8mg/kg, SC; every third day, every other day, but not every day) with HAL attenuated the behavioral supersensitivity. D 2-DAr binding assays showed 1) that CLG-induced changes in B max parallel these behavioral changes and 2) that the biphasic CLG dose-response curve may involve CLG failure at high cumulative doses to lower B max. CLG also reversed an already established D 2 DAr supersensitivity/upregulation (i.e., when CLG was injected daily for four days after the withdrawal or HAL). CLG alone did not alter behavior or binding. CLG's ability to both prevent and reverse D 2 DAr upregulation/supersensitivity in animal models suggests that CLG may be useful, within a therapeutic window, in clinical disorders that are thought to involve upregulated DAr (e.g., tardive dyskinesia, L-DOPA-induced dyskinesias, and schizophrenia).

Evidence for the behavioral supersensitivity of dopamine D 2 receptors without receptor up-regulation in morphine-abstinent rats

The effect of morphine tolerance-dependence and abstinence on the characteristics of dopamine D 2 receptors in brain regions and spinal cord was determined in the rat. Male Sprague-Dawley rats were implanted s.c. under light ether anesthesia with 6 morphine pellets for a 7-day period, each containing 75 mg of morphine free base. Rats implanted with placebo served as controls. This procedure resulted in the development of tolerance to morphine as evidenced by decreased analgesic response to a challenge dose of morphine. Similarly, the development of physical dependence was evidenced by a decreased in body weight and colonic temperature after morphine pellet removal (withdrawal). The binding characteristics ( B max and K d values) of [ 3H]spiroperidol to dopamine D 2 receptors were determined in the tissues of morphine-tolerant and morphine-abstinent rats. In the tolerant rats, the pellets were left intact at the time of sacrificing, whereas, in the abstinent rats the pellets were removed 18 h prior to sacrificing. The binding of [ 3H]spiroperidol was determined in membranes prepared from brain regions (hypothalamus, hippocampus, cortex, pons and medulla, midbrain, corpus striatum and amygdala) and spinal cord of rats from various treatment groups. [ 3H]Spiroperidol bound to brain regions and spinal cord at a single high affinity site. The B max or the K d values in brain regions and spinal cord of morphine-tolerant and -abstinent rats did not differ from their respective placebo controls. The behavioral responses to a selective dopamine D 2 receptor agonist, 2-bromo-α-ergocryptine were also determined in the morphine-abstinent rats. In morphine-abstinent rats, increased behavioral activity, such as total distance travelled, number of movements, and the number of stereotypic movements was seen as compared to placebo controls. The dose of 2-bromo-α-ergocryptine which by itself had no effect on any type of behavioral activity in placebo-treated rats, increased the total distance travelled, horizontal activity, number of movements, and movement time in morphine-abstinent rats. Although in morphine-tolerant or morphine-abstinent rats, the characteristics of [ 3H]spiroperidol binding to dopamine D 2 receptors in brain regions and spinal cord were unchanged, the supersensitivity was observed to behavioral responses of 2-bromo-α-ergocryptine, a selective dopamine D 2 receptor agonist. These results provide an evidence for behavioral responses of 2-bromo-α-ergocryptine, a selective up-regulation in morphine abstinent rats. Previously, we have show that dopamine D 1 receptors are unaffected in morphine tolerant rats but are modified in morphine-abstinent rats. Thus, in the morphine abstinent process a significant difference was noted in the biochemical characteristics of dopamine D 1 and D 2 receptors.

Chronic treatment with MK-801 decreases D 2 dopamine receptor function in rat striatum

Present results show that a single treatment with dizocilpine (MK-801, 0.25 mg/kg IP) failed to modify the specific binding to D 1 or D 2 DA receptors. In contrast, repeated administrations for 3 weeks resulted in a statistically significant decrease of [ 3H]Spiroperidol binding to cortical or striatal membranes but did not change the number or the apparent affinity of [ 3H]MK-801 binding in well-washed cortical membranes. Consistent reduction in specific D 2 receptor mediated behavior was obtained. The data suggest that the changes in DAergic function following repeated administrations with MK-801 could be suggestive of potential therapeutic uses of negative allosteric drugs in some DA related disfunctions.